1. Field of the Invention
The present invention relates to an illumination apparatus using a light guide.
2. Related Background Art
As a conventional image reading apparatus for reading an original image, there is a contact type image sensor which contacts with an original and scans the original to read an image. One example of an illumination apparatus for use in such contact type image sensor is shown in FIGS. 18, 19 and 20. FIG. 18 is a perspective view, FIG. 19 is a sectional view, and FIG. 20 is a view of an end surface viewed from a longitudinal direction.
In FIG. 18, light radiated from a light emitting element 1 such as LED as a light source disposed on an end surface 12 of a light guide 2 is incident upon the inside of the light guide 2, repeatedly reflected by the inner face of the light guide 2 and thereby guided in the longitudinal direction of the light guide 2. A part of the light guide 2 is provided with a diffusing surface 4 for diffusing and/or reflecting the light incident along the longitudinal direction. Then as shown in FIG. 19, when the light repeatedly reflected by the inner face in the longitudinal direction is incident upon the diffusing surface 4, the incident light is scattered, a part of the light radiates from a radiating surface 13 of the light guide 2, and contributes to the illumination of the original as illumination light.
However, in the above-described conventional illumination apparatus, since there is a large amount of light directly incident upon the diffusing surface in the vicinity of the light emitting element in the light guide, and the regular reflected light from the diffusing surface contributes as the illumination light to the object to be illuminated, the illuminance of the vicinity of the light emitting element is higher than that of other areas, and a problem arises that non uniformity is caused in the illuminance of the longitudinal direction of the light guide.
Moreover, there is one example of a conventional contact type image sensor as shown in FIG. 21.
In FIG. 21, the light radiated from the light source 1 constituted of the light emitting elements such as LED disposed on the end surface of the light guide 2 is incident upon the inside of the light guide 2, repeatedly reflected by the inner face of the light guide 2 and thereby guided in the longitudinal direction of the light guide 2. A part of the light guide 2 is provided with the diffusing surface 4 along the longitudinal direction, the light repeatedly reflected by the inner face in the longitudinal direction is scattered upon incidence on the diffusing surface 4, and a part of the light contributes as the illumination light to illuminate the original.
Here, a light guide cover 3 as shown in FIG. 22 is disposed outside the light guide 2 to enhance the light utilization efficiency, and attached so as to cover the light guide via an air layer so that the light leaking from the light guide 2 in a direction different from the original irradiation direction is returned into the light guide. To this end, the light guide cover 3 is formed, for example, of a white material with high light reflecting properties. An original (not shown) positioned on a read line 6 is irradiated with the light radiated from a radiating surface 5 (the surface of the light guide 2 radiating the light which contributes to the lighting of the original as the object to be illuminated) of the light guide 2 in an opening 16 of the light guide cover 3, and the reflected light is formed into an image by a rod lens array 7 on a line sensor 11 disposed on a sensor array 9. When the line sensor 11 converts the information of the light formed into the image to an electric signal and outputs the signal, the reading of the original is carried out.
FIG. 23 is a view only showing the light guide 2 having LED 1 in its end portion and the light guide cover 3. Since the light guide cover 3 covering the light guide 2 is manufactured mainly by injection molding, one side in a metal mold extracting direction forms an opening to extract the metal mold. Therefore, the opening of the light guide cover 3 is larger than the radiating surface 5 of the light guide 2, and the light not contributing to the illumination of the original as the object to be illuminated leaks from the side surface 12 of the light guide 2, which is a large cause for a decrease of the light utilization efficiency.